[Objective] The spatial distribution of soil moisture and the determination of representative sample points under the infiltration irrigation system of plastic film mulching in semi-arid area was studied in order to provide scientific support for orchard water management in semi-arid area.[Methods] Taking the 4-year-old red plum apricot trees under the infiltration irrigation system of mulching rainwater in Pengbao Town, Yuanzhou District, Guyuan City, Ningxia Hui Autonomous Region as the research objects, based on the analysis of soil water distribution characteristics and time stability, the measuring points which could represent the soil profile moisture content around fruit trees were determined by mathematical statistics method, and the relationship between soil water content and representative sampling points were constructed in order to reduce the number and cost of monitoring points.[Results] ① The vertical and radial distribution characteristics of soil moisture were basically the same, the water content first increased and then decreased with the increase of soil depth and diameter distance.The variation coefficient of vertical soil moisture gradually decreased from 30 cm of the first infiltration point to the top, then increased and then decreased. The farther the radial soil moisture was from the infiltration irrigation device, the smaller the variation coefficient was. ② Through time stability, one sample was selected as the representative sample point in humid area. Trough the correlation and cluster analysis of the relationship between the vertical measurement points where the sample was located, it was concluded that the soil moisture content of the 3 representive monitoring points can represent the water content of the whole 0-60 cm depth profile. And verified by the measured data, the water content error was within ±5%.[Conclusion] The distribution characteristics of soil water content in all directions are basically the same. The 3 monitoring points are representative samples of the whole 0-60 cm depth profile.